1. Field of the Invention
The present invention relates generally to microfluidic devices and analysis methods, and more particularly, to microfluidic devices and methods for the manipulation, amplification and analysis of fluid samples including, for example, blood platelet bacteria assays and antiglobulin testing.
2. Description of the Related Art
Microfluidic devices have become popular in recent years for performing analytical testing. Using tools developed by the semiconductor industry to miniaturize electronics, it has become possible to fabricate intricate fluid systems that can be inexpensively mass-produced. Systems have been developed to perform a variety of analytical techniques for the acquisition and processing of information.
The ability to perform analyses microfluidically provides substantial advantages of throughput, reagent consumption, and automatability. Another advantage of microfluidic systems is the ability to integrate a plurality of different operations in a single “lap-on-a-chip” device for performing processing of reactants for analysis and/or synthesis.
Microfluidic devices may be constructed in a multi-layer laminated structure wherein each layer has channels and structures fabricated from a laminate material to form microscale voids or channels where fluids flow. A microscale or microfluidic channel is generally defined as a fluid passage which has at least one internal cross-sectional dimension that is less than 500 μm and typically between about 0.1 μm and about 500 μm.
U.S. Pat. No. 5,716,852, which patent is hereby incorporated by reference in its entirety, is an example of a microfluidic device. The '852 patent teaches a microfluidic system for detecting the presence of analyte particles in a sample stream using a laminar flow channel having at least two input channels which provide an indicator stream and a sample stream, where the laminar flow channel has a depth sufficiently small to allow laminar flow of the streams and length sufficient to allow diffusion of particles of the analyte into the indicator stream to form a detection area, and having an outlet out of the channel to form a single mixed stream. This device, which is known as a T-Sensor, allows the movement of different fluidic layers next to each other within a channel without mixing other than by diffusion. A sample stream, such as whole blood, a receptor stream, such as an indicator solution, and a reference stream, which may be a known analyte standard, are introduced into a common microfluidic channel within the T-Sensor, and the streams flow next to each other until they exit the channel. Smaller particles, such as ions or small proteins, diffuse rapidly across the fluid boundaries, whereas larger molecules diffuse more slowly. Large particles, such as blood cells, show no significant diffusion within the time the two flow streams are in contact.
Typically, microfluidic systems require some type of external fluidic driver to function, such as piezoelectric pumps, micro-syringe pumps, electroosmotic pumps, and the like. However, in U.S. patent application Ser. No. 09/684,094, which application is assigned to the assignee of the present invention and is hereby incorporated by reference in its entirety, microfluidic systems are described which are completely driven by inherently available internal forces such as gravity, hydrostatic pressure, capillary force, absorption by porous material or chemically induced pressures or vacuums.
In addition, many different types of valves for use in controlling fluids in microscale devices have been developed. For example, U.S. Pat. No. 6,432,212 describes one-way valves for use in laminated microfluidic structures, U.S. Pat. No. 6,581,899 describes ball bearing valves for use in laminated microfluidic structures, and U.S. patent application Ser. No. 10/114,890, which application is assigned to the assignee of the present invention, describes a pneumatic valve interface, also known as a zero dead volume valve, for use in laminated microfluidic structures. The foregoing patents and patent applications are hereby incorporated by reference in their entirety.
Although there have been many advances in the field, there remains a need for new and improved microfluidic devices for manipulating, amplifying and analyzing fluid samples.
One example of an area needing new and improved microfluidic devices is with respect to bacterial and antiglobulin analysis. Bacterial sepsis caused by bacterially contaminated platelets is the cause of blood transfusion transmitted infections up to 250 times more often than HIV, hepatitis C or West Nile virus. Of the 4 million platelet units transfused each year in the United States, 1,000 to 4,000 are contaminated with bacteria, and 167 to 1,000 cases of clinical sepsis result. Twenty to 40 percent of patients with clinical symptoms die.
Current Platelet Bacteria Assays
Platelet screening is not routinely performed in the US prior to transfusion; however, AABB has proposed a new standard requiring pre-transfusion testing of platelets for bacterial contamination.
Several methods are currently being used outside the US:                Standard cell culture: platelets are cultured in Petri-dish, and bacteria are detected after staining. This method is very time consuming, is not automated, and requires a significant amount of platelets.        Pall Bacteria Detection System (Pall BDS): uses changes in oxygen concentration as a result of bacterial growth. Since bacteria consume oxygen, abnormally low levels of oxygen in a platelet sample indicate the presence of bacteria.        BioMéneux's BacT/Alert system detects the presence of bacteria by tracking their production of carbon dioxide.        Hemosystem is developing a system for bacterial detection in platelets concentrates based on fluorescence detection after bacteria labeling with a fluorescent marker.        